This invention relates generally to compass apparatus and, more particularly, to compass apparatus of the type wherein a compass card member is rotatably disposed within a liquid-filled space defined within a housing having a transparent hemispherical or cupola-shaped cover portion.
Compass apparatus including a compass card member rotatably disposed within a liquid-filled space defined within a housing having an upper transparent cupola-shaped cover portion, hereinafter referred to as a cupola compass, are known. For example, a cupola compass apparatus is disclosed in Swedish Pat. No. 318,418 which includes a pair of hemispherically shaped members sealingly connected to define a liquid-tight interior in which a compass card member is rotatably mounted in an appropriate fluid. The hemispherical members are provided with peripherally extending flanges which are sealingly joined by a resilient sealed ring having a substantially V-shaped cross section. The V-shaped sealing ring sealingly couples the respective peripheral flanges of the pair of hemispherical members by means of two connecting yokes having a U-shaped cross section. However, the connecting yokes are permanently clamped in position in a manner such that the compass housing cannot be opened. Further, the hemispherically shaped housing members are formed of rigid, inelastic material and, for this reason, the V-shaped sealing ring has elastic properties which permits the capacity of the liquid-containing housing interior to change as the volume of the fluid in which the compass card member is disposed itself changes as a result, for example, of temperature changes.
Thus, the general state of the prior art is such that it is desireable to provide cupola compass apparatus which is both simple in construction and economical in manufacture and wherein access to the interior thereof is possible even after the hemispherical members are sealingly joined to each other so that the compass card member can be repaired.